The present invention relates generally to filler materials for implantable prostheses for use in plastic and reconstructive surgery, as might be particularly useful in breast reconstruction and augmentation.
Subcutaneous reconstructive implant procedures for augmenting or reconstructing certain soft tissues in humans, including breast and facial implants, have been in wide use since at least the early 1960s. The implants consist of hollow, physiological shells filled with a filler material. The physiological shells are typically formed from silicone rubber or other elastic biocompatible materials which have enough memory to preserve a desired shape. In order to minimize the risk of leakage, the physiological shell often consists of multiple layers.
Controversy has surrounded the materials used to fill the physiological shells. One filling material that was previously quite popular was silicone gel. However, the use of silicone gel is associated with a number of problems. For example, silicone gel is not sufficiently radiolucent and can thus obscure mammographic signs of breast cancer. In fact, some researchers have suggested that breast implants containing silicone gel fillers prevent early detection of breast cancer and hence reduce the probability of a promising prognosis once cancer is detected. Because an estimated one in nine women will develop breast cancer, and, with cancer recurring in another 1 in 3, the risk of delay of detection caused by silicone gel implants is quite significant. Another problem with silicone gel fillers is that the body is unable to metabolize or excrete the silicone gel. In the event of a leak from the shell, the silicone gel is apt to migrate or leak into surrounding tissue where an undesirable body reaction can ensue, thereby requiring surgical removal or other treatment.
In recent years, saline has supplanted silicone gels as the most prevalent implant filler material. However, saline is also ill-suited for use as an implant filler material. Significantly, saline has a relatively low viscosity and is a poor lubricant thereby resulting in an excessively soft implant that is prone to rippling, fold flaws and spontaneous deflation. Saline fillers also suffer from an unnatural "feel." In the event of containment sac perforation, filler escape is immediate with spontaneous deflation. Further, if air enters the containment sac during filling, a postoperative audible noise may result.
Other previous approaches have involved the use of soybean oil, hyaluronic acid and polyethylene glycol. However, the long-term safety and stability of these materials has yet to be determined. For example, breakdown of the materials when implanted is unknown. Soybean oil has the added problem of being difficult to intraoperatively inject into the containment sac. In the case of hyaluronic acid, the interaction of the filler material with the containment sac is not established.
In addition, in U.S. Pat. No. 5,067,965, Ersek, et al., propose a bio-osmotic gel material comprising polyvinylpyrrolidone for use as an implant filler material. However, the materials disclosed by Ersek, et al., are quite expensive and are not capable of injection, thereby requiring filling prior to implantation. As such, the filler materials of Ersek, et al., do not permit modification of the filling procedure following implantation in situations where the initial filling operation proves to be unsatisfactory.
Despite the availability of the foregoing approaches, it will be appreciated that there still exists a need in the art for implant filler materials which are relatively inexpensive, radiolucent, physiologically absorbable, and which have a sufficient viscosity to minimize the risk of deflation. There also exists a need for implant filler materials that can be injected into the physiological shell either before, during, or after the surgical implantation procedure.